GROWTH AND ENERGETICS IN THE ASCIDIAN CIONA-INTESTINALIS

Rates of growth, filtration and respiration of the ascidian Ciona inte stinalis (L.) were measured in the laboratory in the presence of food (flagellate Rhodomonas sp.) concentrations ranging from 0 to 12 000 ce lls ml(-1) (0 to 500 mu g C l(-1)). Weight-specific growth rate (dry w eight of body parts not including the tunic) increased sigmoidally wit h increasing algal cell concentration to 7.7% d(-1). Maximum specific growth rate was related to age rather than size. A condition index (CI = DWbody/DWtotal) reflected level of growth. Specific filtration rate decreased logarithmically with increased algal cell concentration. We ight-specific respiration rate showed a relation to algal cell concent ration similar to that shown by weight-specific growth rate. All rates were transformed into units of carbon, and a carbon budget was establ ished for 2 size groups. Assimilation efficiency (AE) was approximatel y 50% but decreased at the highest carbon concentrations. The amount o f carbon assimilated per body unit that was needed to maintain body (n ot including the tunic) or total (including the tunic) carbon was inde pendent of initial size and amounted to 10 or 16 mu g C mg C-1 d(-1), respectively. Gross growth efficiency (GGE) and net growth efficiency (NGE) Varied with food concentration and approached a level of 0.23 or 0.78, respectively, in terms of body carbon. In terms of total carbon , GGE was found to be 0.27 to 0.28 and NGE to be 0.79. Costs of mainte nance were greater in the largest ascidians, while costs of body growt h were equal in the 2 size groups (0.21 to 0.23).